The invention relates to a boost style DC/DC converter for biasing capacitive sensors of MEMS microphones, specifically a MEMS boost style DC/DC converter including an integrated inductor.
MEMS microphones use charge pumps to boost the bias voltage applied to a capacitive sensor above the power supply voltage. Charge pump designs cascade a series of pump blocks that build on the input voltage from a prior stage. Each stage's gain is limited to something less than the power supply's voltage, ideally a supply and temperature-independent reference voltage. For low-voltage designs that are required in the cell phone market, such as a 1.5 volt power source generating greater than 50 volts, a large number of stages are required. This results in higher current consumption because of parasitic capacitances generated by the charging and discharging of each stage. In addition, the large number of stages requires a large silicon foot print.
In addition, high-voltage charge pumps require high-voltage components or standard CMOS components placed in high-voltage isolation wells, both having relatively large space requirements. Also, because the capacitors need to tolerate high voltage, the capacitors are metal-metal capacitors. Metal-metal capacitors have relatively low density, which increases chip real estate requirements and cost.